High-pressure petroleum gas dispensing method and apparatus



Sept. 14, 1948. R HOLICER 2,449,118

HIGH-PRESSURE PETROLEUM GAS DISPENSING METHOD Km) APPARATUS Filed Nov. 13, 1945 2 Sheets-Shem: 1

IN V EN TOR John 12. Hall-c gz'azm 4; w

J. R. HOLICER HIGH-PRESSURE PETROLEUM GAS DISPENSING .sem. M, 1%.

METHOD AND APPARATUS 2 Shaets-$heet 2 Filed Nov. 13, 1.943

INVENTOR. 1:5, I John Q. Ho/icer da/9J4;

Patented Sept. 14, 1948 mGH-PRESSURE PETROLEUM GAS D- PENSING ME'XHCW AND APPARATUS John R. liolicer, Shreveport, La.

Application November is, i943, Serial No. 510,228

ii Claims. (Cl. 62-3.)

This invention has to do with method and apparatus for storing, releasing and dispensing fuel gas of the general character of propane by temporarily reducing the normal vapor pressure of such gas so that it may be safely contained in apparatus designed to withstand only relatively low pressure.

Whether used in presently existing apparatus or in new equipment specially built, high pressure gases emanating from liquefied petroleum gas fuels may be safely handled in relatively inexpensive low pressure containers through the prac tics of the method here disclosed.

The method and apparatus of this invention are particularly well adapted for the safe handling of relatively high pressure gases through the utilization of presently existing gas storage and dispensing equipment heretofore employed in the handling of such relatively low pressure gases as butane.

Many thousands of butane gas storage, generating and dispensing systems haveheretofore come into quite common use. Ordinarily these systems have been employed for containing and conditioning butane gas for the reason that butane has been generally available, and for the further reason that it is a combustible hydrocarbon fiuid easily liquefied by being reduced to a temperature of approximately 32 degrees Fahrenheit, or by being subjected to relatively little pressure. Such fluid is readily converted into usable gas fuel by allowing it to absorb latent heat from the earth in storage tanks ordinarily buried in the ground. When this fuel is thus generated into gas, it exerts a relatively low pressure, depending upon its temperature. For instance, at 100 degrees Fahrenheit the pressure indicated is 37.5 pounds per square inch. Con tainers for butane have therefore been designed and made of relatively light weight material, allowing a reasonable safety factor over actual working pressure.

However, such containers were not built to withstand the normal gas pressure of propane.

At 100 degrees Fahrenheit propane has a pres- 7 sure of 172 pounds per square inch. This is somewhat above the safe working pressure of the vessels designed to contain butane. Therefore. the use of propane in such vessels is dangerous and unsafe.

The economic disruption incident to the present world war and the military and technical needs for butane in the manufacture of synthetic rubber and high octane gasoline have to a great extent made butane unavailable for domestic M uses and for most of the ordinary industrial uses, as fuel.

Therefore, a great quantity of very good storage and dispensing apparatus ordinarily designed for liquefied petroleum gases of relatively low pressure such as butane is in disuse, resulting in a vast economic loss to the country and considerable discomfort on the part of many thousands of its citizens.

Various have been the attempts to utilize this old equipment for the handling of propane; but such efforts have not been satisfactory. If straight propane is used to charge such old vessels, it will result in their rupture: and frequent explosions and fires, with loss of life and property, have come out of such attempts. It is to be noted that propane is generally available for domestic and ordinary industrial fuel demands: but to use it in orthodox manner requires completely new equipment capable of withstanding relatively high pressure. Such equipment is not available, nor are the materials for building it.

The present art on this subject reflects that expedients have been resorted to for the purpose of confining propane in these old low pressure tanks; but none have been very satisfactory. For instance, a charge of gasoline has been premixed with propane so that the resultant mixture is a liquid which will possess a relatively low vapor pressure. This mixture is then put in the old butane storage tank; and from this tank the propane liberated by the heat of the earth will be drawn off as used. It is to be noted that such a mixture inhibits the normal vapor pressure incident to the use of straight propane, and thus the vessel is rendered relatively safe from rupture.

However, such expedlents have employed what is known as the "batch" system, requiring the mixture of gasoline and "propane at the plant of the supplier of fuels; and thereafter the mixture has been trucked to the consumer's premises in high pressure tanks and delivered to his private underground storage as a mixed liquid under pressure. This results in the. useless trucking to the premises of a considerable quantity of unusable gasoline.

Furthermore, after the batch of mixed fuel with which the storage tank has been charged has served its purpose by allowing the withdrawal therefrom over a period of time of the liberated propane gas as it is needed for fuel. there remains in the storage tank a considerable quantity of gasoline which serves no further useful purpose inthetankandhastobewithdrawnandtaken 3 back to the mixing plant for the measured adding of propane, with a double expense in labor and trucking.

Moreover, the removal of this residual gasoline is fraught with the danger of fires and explosions because of its highly inflammable and explosive character; and the withdrawal of such gasoline on the premises of the householder presents a distinct fire hazard to his house and premises.

It has not been found at all practical or safe to periodically bring further gasoline upon the premises to replenish that which has been vaporized and consumed as gas along with the propane. The old storage tank has to be opened and gaged to determine what quantum of new gasoline is required; and furthermore, the mixing of propane with gasoline on the premises is dangerous because both are highly explosive.

This unsatisfactory condition arises because there is a constant diminution of the gasoline in the storage tank. The heat of the earth around the storage and the agitation it causes within the vessel during the period and process of the liberation of propane carries over a certain quantity of gasoline, as vapor, into the home or premises of the user. Frequently this gasoline liquefies on the way to the burners of the gas consuming appliances and even in these appliances; and not infrequently such gasoline in liquid form accumulates within the burners, valves and conductors in the walls and rooms where the gas burning appliances are housed. Such undesirable result is too dangerous to countenance.

A primary object of the method and apparatus here disclosed is to present a safe means for using old storage and dispensing equipment of low pressure character, ordinarily and generally characterized as butane systems; and one essential object is to utilize such equipment for the handling, storing and dispensing of propane gas and gas of such general character.

Another object of considerable importance is to provide a method whereby this old equipment may be used with absolute safety, so that the vessels thereof will not rupture and there will be no fires and explosions resulting.

'A very definite object of this invention is to provide a method using a liquid absorbing medium for temporarily containing propane in a reversible union therewith, which will at once absorb the propane and lessen the vapor pressure of the resultant mixture below that of straight propane.

An important object is the provision of a method wherein the absorbing medium is constant in quantity in the system, undiminished by use as a carrier of propane, and capable of taking a given charge of propane when the previous charge is exhausted, without need to periodically measure, replenish or remove the absorbent.

A highly valued object is attained by providing method and apparatus using, as an absorbent for propane, a liquid which will readily receive propane when the latter is allowed to bubble up through it, and as readily release the propane when the mixture is conducted to a separating chamber maintained at a controlled temperature sufiicient to instantly translate the propane into gas without vaporizing any part of the absorbing liquid. Therefore, the use of an absorbing liquid which will not be vaporized at temperatures which will release propane therefrom is important.

A further and valued object of the invention is to provide method and apparatus for effecting low vapor pressure of a mixture of an absorbing 4 liquid and propane, releasing the propane from the mixture within a heated chamber, and allowing the absorbing liquid to freely return to the storage tank from which the mixture emanated, thus presenting a continuous system, which may be further appropriately described as a re-cycling system.

Another object is to provide automatic valve means whereby the direction of the continuous fiow of the mixture is controlled, and also the direction of the return of the absorbing medium to the storage tank is controlled.

Of further importance is the object of providing means whereby a heated gas separating chamber, distinct and apart from the storage tank with which it communicates, will never be allowed to fill with absorbing liquid and overflow therefrom will be positively prevented.

Further objects are realized in the character of the means employed to prevent the filling oi the separating chamber; and such means may be found in the elevation of the separating chamber above the level of the storage tank, or in thermal controlled means or in float controlled means.

Numerous arrangements and dispositions can be made of the component parts of this invention and system and still preserve the method here set forth. However, preferred forms of mechanism satisfactory for the practice of this invention are set out in the drawings, in which:

Fig. I is an elevation of a typical mixing and storage tank and apparatus for circulating, heating and separating mixed liquid from the tank. The tank is partially cut away to show the filling,

. discharge and return pipes and fittings.

Fig. II is a sectionallzed elevation of a typical separating chamber with heat exchanger, heater and thermal control mechanism.

Fig. III is a sectionalized elevation of a separating chamber provided with float control mechanism.

In the details of the drawings the numeral l indicates a typical storage tank, usually found buried underground. It will be economical to utilize presently existing storage tanks which have heretofore been used for butane storage and generation of the dry gas from the liquefied gas with which the tank has been customarily charged. Butane being unavailable to a great extent, many of these tanks are unused but still in excellent condition and usable if care is taken to see that they are not subjected to a greater pressure than*their safe working pressure. course, in the operation of this system, such a tank could be provided new, if desired; and the method could be practiced equally well therewith.

' Numeral 2 represents a control head fitted intoan opening in the top of the storage tank for carrying requisite fittings to fill and discharge the tank and to receive the return of absorbent liquid thereto.

The filling line isequipped with a cap I which can be removed to provide screw connection for a hose to receive liquefied gas under pressure. Below the control head there is provided a filling valve 4 and a back flow check valve 5. These two valves, as well as the control head itself, may be constructed substantially as disclosed in my co-pending application heretofore filed under Serial No. 501,019. It is desirable, however, that the filling pipe 6, which communicates with these valves within the tank, extend downwardly in the tank to a point near its bottom. Such construction will inhibit the separation of volatile liquefied hydro-carbon gas such as propane, with which this tank will be periodically charged, by being thus introduced below the level of an absorbing liquid carried constantly in the storage tank. That is to say, it is desirable to introduce the liquefied propane into the bottom of the tank so that it may bubble up through the absorbing liquid, the better to be absorbed thereby.

This absorbing liquid remains stable and in liquid form at all times during the practice of the method here disclosed, and it will not be vaporized at temperatures which will release the propane mixed therewith; but it will be of a character capable of readily absorbing propane. Such an absorbent liquid may be produced in the distillation of petroleum, and it will be considerably heavier in gravity than gasoline. An appropriate absorbent is such a derivative known as furnace oil which is occasionally referred to as straw-colored distillate.

The heat of the earth in which storage tank I is buried below the frost line is suflicient to cause the mixture in the tank to exert some pressure; and this pressure is enough to allow the discharge from the tank of the mixture in liquidform through the eduction line I, the open end of which is near the bottom of the storage tank. This line is carried in the control head in an opening therethrough and continues thereabove as a conduit having a manually operated control valve 9 therein. This eduction line is provided with an excess flow check valve 8 of any appropriate design, but which may be constructed according to the disclosure thereof in my aforesaid co-pending application. This excess flow check valve normally remains open and will allow the flow of a sufficient quantity of liquid mixture out of the tank when valve 9 is open; but it will close immediately if such valve is accidentally broken oil or the conduit ill with which it communicates is broken.

Conduit Hi conducts the liquid mixture from' the storage tank to a separating chamber; and the conduit has a check valve ll mounted therein which will allow the liquid to flow in one direction only, that is, from the storage tank and to the separating chamber I2.

Within this chamber, which is provided with a heat exchanger I3, the mixed fluid is separated into its component parts by reason of the temperature at which the chamber is maintained. The propane, being highly volatile and very light in character, instantly rises to the top of the chamber from which it may pass outwardly through gas service pipe H which conducts the gas to gas consuming appliances for consumption.

The absorbing liquid remaining in the separating chamber, after the volatile gas has been separated from the mixture, will pass through an opening I in the bottom of the chamber and into return pipe l8 which will carry it back into the storage tank from which it emanated.

This return pipe is provided with a check valve II which will allow the liquid to return to the tank, but which will prevent any liquid from passing upward from the tank into the chamber.

The returning liquid may be discharged into the tank at any convenient place; but it is desirable that it enter the tOp of the tank and there be discharged, for the reason that the returning absorbent will pass through an area of gas in the top of the tank and effect the reduction of some portion thereof to liquid. A simple spray head II should be attached to the discharge outlet of return pipe l6 below the control head 2, so that the absorbent will settle down into the tank from above in the form of a spray, the better to absorb the gas in that part of the tank. The absorption of such gas will aid in maintaining the tank at relatively low pressure.

It will be seen from the foregoing that the absorbing medium continues to flow in a cycle. First it leaves the storage tank, carrying with it a quantity of propane which it has absorbed; and then the mixed gas and absorbent is delivered to the separating chamber by the expelling pressure within the storage tank. From this chamber the propane does not return to storage. It is delivered through gas service pipe H to the gas consuming appliances when and as fuel demands require. Finally the absorbent, which is a relatively heavy fluid, returns to the storage tank after being relieved of its ireight'of light gas, so that it may pick up a further charge of gas for delivery to the separating chamber:

Thus is practiced a re-cycling method in which the absorbent continues to circulate and flow so as to absorb and later release propane for use. The quantum of this circulating absorbing liquid continues constant, and its capacity to absorb and discharge volatile petroleum gases is undiminished.

The separating chamber l2 may be heated in any convenient manner, such as by the use of the heat exchanger l3, or by the direct application of heat. A heating jacket surrounding the chamber admirably serves this purpose; and

through this heating jacket may be circulated a warm fluid. Such a fluid may be aliquid which is not easily reduced by evaporation and which has a low freezing point, so that it is not adversely affected by variations in atmospheric temperature. Asuitable petroleum distillate may be employed for this purpose; and, of course, water may be used.

The fluid medium which circulates through the heat exchanger is kept warm by an appropriate heating device such as that disclosed, wherein a heating coil I9 is disposed within a jacket to form a heater 20; and this coil discharges heated fluid through pipe 2| into the heat exchanger, and receives therefrom the return of the fluid through pipe 22. It is usual to provide the heater with a vent 23.

The heater may be gas fired, and gas can be conducted to it through gas pipe 24 which delivers this fuel to the burner 25. A pilot tube 26 is provided to supply gas to pilot 21.

It is desirable to maintain the heat in the separating chamber at a constant temperature, or within a temperature range which will allow the free release of propane from the mixture in the chamber but which will not be sufilcient to convert the absorbent into gas. For this purpose, a commercial thermostat 28 is provided in gas pipe 24 to control the quantity of fuel going to burner 25.

Any thermostat ordinarily to be found on the market will serve the purpose here required. The one indicated is of conventional designand provides a tube 29 within the heat exchanger jacket; and it is immersed in the circulating fluid. This tube is of metal and encases a metallic rod which has greater expansion capacity than its casing. When heated to a pre-determined temperature, the rod extends and closes a valve carried within 7 the body oi the thermostat. when the temperature within the heat exchanger drops, the rod cools and re-opens the valve so that gas will flow again to the burner where it will be ignited by the pilot 21.

It has been determined that the system as outlined above will work in a very satisfactory manner without any further controls. This is especially true when the separating chamber is elevated somewhat above the level of the storage tank. Usually the latter is underground, and the former is Just above the level of the earth. This arrangement would allow the gas pressure within the storage tank to force the mixture into the separating chamber and, at the same time, the elevation of the latter will allow the return of the absorbing liquid to storage.

However, a safety measure may be provided which will prevent the flow of any mixed fluid into the separating chamber should the chamber become cold through the failure of the heat exchanger to work for any reason.

For this purpose there has been provided a thermocouple valve in discharge pipe ID. This valve has within its body spring closing means which normally keeps the valve closed; but the thermal operated device will maintain the valve in open position as long as the pilot 2'! is lighted. This is accomplished by the use of a thermocouple lead 3| which communicates with the spring closing means in the body of the valve and extends to a thermocouple 32 placed in immediate proximity to the pilot flame. The thermocouple is made of expansible material which, when heated, will extend a member within the lead so as to open the valve. There are several thermocouple valves of this general character on the market which will serve the purpose here indicated; and among them is the device having the trade mark Baso" made by the Milwaukee Gas Specialty Compam'; and it will serve the purpose.

With the use of the thermal control indicated, it will be seen that, regardless of the positioning of the separating chamber with reference to the storage tank, there can be no over-filling of the separating chamber with the mixture. The chamber is maintained at that temperature which will immediately translate the propane into usable dry gas and allow the constant return to the storage tank of the absorbing fluid from which it is released. If perchance the pilot light should o out, no more mixture can thereafter flow to the separating chamber until after the pilot has been lighted and until its flame has continued long enough to operate the thermocouple valve.

Three separate and distinct arrangements have been made which will afl'ord control to prevent overflow of the separating chamber. One employs the elevation of the latter above the levelof the storage tank. The second provides the use of the thermal control herein disclosed for that purpose; or a third arrangement can be provided to effect this object, as follows:

In Figure 3 is disclosed a float control construction wherein float 33 is disposed within the separating chamber; and extending above the float there is control rod 34 which passes through opening 35 in control lever 36. This lever is mounted upon a fulcrum pin 31, so that when the free end of the lever is elevated by the rising of the float, the valve disc 38. carried by the opposite end of the lever, is brought into engagement with valve seat 39 provided in the body of float valve 40. This valve communicates with the separating chamber through its upper side wall and- 8 connects to conduit id to receive the liquid mixture coming from the storage tank.

Whenever the float rises to a pre-determined height, shoulder 4| on the topmost part of the float engages lever 36 and lifts it, thus closing valve 40; and thereafter no further liquid can enter the separating chamber until the excess liquid accumulated therein has passed downwardly through return pipe l6. In order to the proper alignment of the float and to maintain it in proper working position. there is extended directly below and from which extends for a distance down within pipe i 3.

Around the opening I! in the bottom of the separating chamber through which pipe it communicates with the chamber there is provided valve seat 43. Aligned with this valve seat and carried on the lower part of the float is the circular disc 44 which normally rests upon the valve seat and closes the discharge outlet leading to pipe It. This valve remains closed until a sumcient quantity of liquid accumulates inthe chamber to raise the float.

' Ordinarily the temperature of the chamber is such that only a small quantity of liquid accumulates, the usual process allowing the prompt return of the liberated and collected absorbent to the storage tank after the instant release therefrom of the propane which it carries. This occurs whenever suflicient liquid is accumulated to raise the float. However, should the temperature of the separating chamber drop to a point that this return is not quickly and continuously eifected, the float will rise and close valve ll, which will remain closed until the excess quantity of liquid in the bottom of the separating chamber separating chamber.

has drained oil through pipe ll; or until the chamber is re-heated.

4 The float can be dispensed with. Because the separating chamber is ably higher temperature than the tank,-the mixture entering the chamber instantly releases its gas and builds up the chamber pressure. This pressure closes the check .valve in the incoming conduit, and it opens the check valve in the re,- turn pipe through which the absorbing liquid is forced back to the tank immediately by the higher' pressure. This is a, process which is repeated regularly and operates somewhat like a pump, as long as fuel is being consumed.

The storage tank is replenished with propane whenever the gas is nearly exhausted after repeated circulation of the mixture through the upon the premises by truck, and pumped into the storage tank under pressure. The requisite quantity of propane is measured and delivered into the tank. It is not necessary to measure the absorbing liquid then or at any time, because it is not evaporated and remains constant in quantity, This means that it is not necessary to remove the liquid and transport it to the supplier's place of business for measuring and replenishing. which would be the case if such liquid constantly diminished from use. Therefore, it is not necessary to do the mixing at the supplier's place.

There is no danger in injecting the propane into the liquid in the storage tank on the user's premises. The absorbing liquid does not there have to be mixed in any container before being placed in the storage tank. Furthermore, it is not an explosive or dangerous liquid; and when this miscible liquid receives propane, the resultant the float the guide rod ll.

maintained at aconsider- The propane is brought Q measured; and it need not there be fluid is homogeneous and has a vapor pressure greatly reduced below that of propane alone. This lower pressure is highly desirable. It promotes safety; and it eliminates the possibility of damage to the householders tank and equipment, which would be ever present if propane alone were used.

When the absorbing liquid is spoken of herein, it is intended to comprehend any stable liquid which will freely receive and unite with petroleum gases and which will not be vaporized by heat sufficient to release these gases therefrom.

When propane is spoke of herein, it is intended to comprehend not only propane, but also methane and ethane.

Such gases are readily translated from liquid state to gaseous state when exposed to atmospheric temperatures prevalent in the Temperate and Torrid Zones; and in such locality this system will operate, even when the storage and mixing tank is found above the surface of the earth.

However, it is contemplated that as a matter of practice. the tanks in which this system is to be used will be placed under ground.

It is evident from the above description of this invention that: A continuous process has been achieved whereby gaseous fuel possessing the general characteristics and physical properties of propane gas and somewhat similar hydrocarbon derivatives of petroleum may be readily introduced into mixture with a liquid absorbent capable of receiving and being freighted with such gas; and that the mixing of these two components in exact and proper proportions may be safely and quickly effected on the premises of the consumer and in the storage tank there maintained without any necessity for removing the absorbent or even measuring it at the time the storage tank is to be recharged with the gas; and that the absorbent may be periodically freighted with a pre-determined charge of gas from time to time; and that the absorbing medium will remain constant in quantity over a very long period of time; and that the mixture has a relatively low vapor pressure; and that it may be removed from the storage tank to a relatively small separating chamber, maintained at a controlled temperature sufficient to quickly release the propane as a usable dry gas fuel, and at the same time continuously return to the storage tank for further use as an absorbent the liquid medium from which the gas has been released; and the whole process may be practiced and accomplished without damage to containing vessels, and without danger and annoyance of overfilling the separating chamber with either the mixture or the absorbing liquid and without any part of the latter being allowed to overflow into the householders premises; and that high pressure gas may be safely dispensed from vessels designed for the use of low pressure gas.

I claim:

1. The method of storing and dispensing high pressure petroleum gas, which consists of mixing the gas with a body of stable liquid under pressure. expelling a portion of the mixtureby the pressure of gas emanating from the mixture, collecting the expelled portion in a separating chamber. heating the chamber to liberate the gas from the mixture in the chamber and to increase its pressure, returning the separated liquid to the original body by said increase in pressure, and removing for consumption the liberated gas.

2. The method of storing and dispensing high pressure petroleum gas, which consists of mixing chamber; a check valve in l 10 the gas with a body of stable liquid ,under pressure, expelling a portion ofthe mixture" by the pressure of gas emanating from theiihixtuilte, collecting the expelled portion in a separating chamber, heating the chamber to libcrate'tl ie gas from the mixture in the chamber and to increase its pressure, returning the separated liquid to the original body by said increas in pressure, removing for consumption the liberated gas until pressure in the chamber is reduced below that maintained on the original body, and allowing a new portion of the mixture to again enter the chamber.

3. The method of storing and dispensing high pressure petroleum gas, which consists of mixing the gas with a body of stable i'quid under pressure, expelling a portion of t e mixture by the pressure of gas emanating from the mixture, collecting the expelled. portion in a separating chamber, limiting the quantity of mixture so collected to that which, when heated, will produce a pressure in the chamber exceeding the pressure of the original body, heating said chamber until the mixture therein separates into gas and liquid and the pressure of said gas is sufiicient to force the return of said liquid to the original body, and removing the liberated gas from the chamber.

4. The method of storing and dispensing volatile petroleum gas by introducing it into a storage tank and there mixing it with a stable absorbing liquid, withdrawing the mixture in increments o a separating chamber, controlling its introduction to the chamber by thermal means, heating the chamber until the gas is liberatedfrom the mixture, and returning the liquid to the tank, by

pressure from the liberated gas.

5. The method of storing and dispensing volatile petroleum gas by introducing it into a storage tank and there mixing it with a stable absorbing liquid, withdrawing the mixture to a separating chamber, regulating its intermittent introduction to the chamber by float control, heating the chamber until the gas is liberated from the mixture, and returning the liquid to the tank by pressure from the liberated gas.

6. In apparatus for storing and dispensing high pressure petroleum gas, a mixing and storage tank; a separating chamber; a conduit for delivering liquid from the tank to the chamber; a check valve in the conduit; means for heating the chamber; a service pipe for carrying gas from the chamber; a return pipe adapted to return liquid from the chamber to the tank; and a check valve in the return pipe.

'7. In apparatus for storing and dispensing high pressure petroleum gas, a storage tank buried in the ground and adapted for mixing gas and liquid; an elevated separating chamber; a conduit for delivering fluid from the tank to the the conduit; a float controlled intake valve associated with the chamber and the conduit; means for heating the chamber; a service pipe for carrying gas from the chamber; a pipe adapted to return liquid from the chamber to thetank; and a check valve in the return pipe.

8. In apparatus for storing and dispensing high pressure petroleum gas, a mixing and storage tank; an elevated separating chamber; a conduit for delivering fluid from the tank to the chamber; a check valve in the conduit; a thermal controlled intake valve associated with the chamber and the conduit; means for heating the chamber; a service pipe for carrying gas from the chamber; a pipe adapted to return liquid from 1 1 the chamber tothe tank; and a. check valve in the return pl JOHN R. HOLICER.

REFERENCES CITED The following references are of record In the file of this patent:

Number Abramaon Nov. 30, 1943 

